1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member having a surface protection layer. More particularly, the present invention relates to an electrophotographic photosensitive member having a protection layer containing electroconductive particles which are surface-treated with a specified compound. The present invention further relates to an electrophotographic apparatus, a device unit, and a facsimile machine employing the above electrophotographic photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members are naturally required to have sufficient sensitivity and electrical and optical characteristics necessary for the electrophotographic process to which they are applied. Additionally, the photosensitive member which are used repeatedly are required to be stable to external electrical and mechanical actions such as charging, development, image-transfer, and cleaning. Specifically, the photosensitive members are required to be resistant to wearing and scratching by friction at the surface and to deterioration caused by ozone and NOx. Furthermore, the photosensitive members are required to have excellent cleanability to prevent sticking of a toner on the surface thereof.
A method to satisfy the above-mentioned characteristics required of the photosensitive member is to provide a surface protecting layer mainly composed of a resin on the photosensitive layer. In one example of the protecting layer, a metal oxide is incorporated as an electroconductive powder to control the electric resistance as disclosed in Japanese Patent Application Laid-Open No. 57-30843.
The metal oxide is added to the protecting layer of the electrophotographic photosensitive member mainly for the purpose of controlling the electric resistance of the protecting layer itself to prevent the increase of residual potential in the photosensitive member during repeated use of the electrophotographic process. The protection layer of the electrophotographic photosensitive member has an electric resistance preferably in a range of from 10.sup.10 to 10.sup.15 .OMEGA..multidot.cm. However, the electric resistance is liable to be affected greatly by ionic conduction and tends to change significantly depending on environmental conditions. In particular, the protection layer containing a metal oxide dispersed therein cannot necessarily retain the resistance within the above defined range in all environmental conditions during repeated use in the electrophotographic process because of the hygroscopicity of the surface of the metal oxide.
In the case where a particulate material is dispersed in the protection layer, the particles have desirably a diameter less than the wavelength of incident light, namely less than 0.3 .mu.m to prevent scattering the incident light by the dispersed particles. Fine particles, however, tend generally to aggregate and are not readily uniformly dispersed, and moreover, the particles once dispersed are liable to cause secondary aggregation or sedimentation. Therefore, it was extremely difficult to prepare stably a film that contains fine particles of 0.3 .mu.m or less in diameter dispersed therein. From the standpoint of improving the transparency and the uniformity of electric conduction of the layer, it is desired that ultra-fine particles having a much smaller diameter (primary particle diameter of 0.1 .mu.m or less) are dispersed. However, the dispersibility and the dispersion stability of such ultra-fine particles tend to be lower.
Particularly at high humidity, paper powder, or corona discharge products, such as ozone and NOx, caused by charging are liable to adhere to the surface of the photosensitive member, leading to decrease of the surface resistance, and causing blurring or running of images.
With the recent demand for higher quality of images and higher durability, electrophotographic photosensitive members are being investigated which are capable of giving excellent images more stably under any environmental conditions.